Some types of agricultural crops are harvested primarily for their flowers or for their pre-flowering buds (embryonic shoots). Examples of such crops include hops (one of the four main ingredients in beer), medical marijuana, or recreational marijuana in jurisdictions where it is legal, for example.
The harvesting of such crops typically includes separating the desirable flowers or buds from undesirable leaf material. Conventionally, this is achieved by causing harvested buds to travel longitudinally through the inside of a tumbler, which is conventionally a rotating cylinder formed of sheet metal with slots cut out of it. As the tumbler rotates, a vacuum underneath the tumbler applies a suction force, which causes some of the leaves to protrude outward through the slots into the cylinder and into the path of a sharp cutting blade spinning in close proximity to the cylinder, so that the leaves are trimmed by the blade.